Solar Filter Cleaning Instructions

Glass Solar Filters: Clean only with Isopropyl (rubbing) alcohol and a soft tissue. Apply generous amount of alcohol to the tissue and rub lightly across surface using long strokes. Lightly wipe dry with fresh tissue. Since the coating is on the back side of the glass facing the telescope, it will rarely if ever need cleaning if handled carefully and kept covered when not in use. The outside surface can be cleaned without danger of damaging coating. Loose dust on inside surface can be blown off or lightly dusted with dry cotton.

Pinholes and minor surface scratches are common in solar filters, however, our multi-coating technique keeps them to a minimum. A "bright" pinhole may cause "ghosting" due to scattered light. If this is seen during observation, the pinhole(s) should be blocked out. Blocking out any pinholes should be done on inside coated surface. Hold filter 1-2 feet in front of a standard 60-100 watt "soft white" light bulb. Blocking can be done with a fine point felt marker, small drop of paint, typing correction fluid etc. The touch up procedure will not degrade the optical performance. It is not necessary to touch up any small pinholes that do not cause image problems. There is no danger if some small non light scattering pinholes or minor scratches are present. All filters are tested for safety before shipment.

Black Polymer Solar Filters: One layer design with absorptive filtering material spread throughout substrate. Clean same as glass.

When using low magnification the image may appear bright in some telescopes with optical density 5 filters. Color or polarizing eyepiece filters can be used in addition if desired. The higher the magnification, the dimmer the image will become. Binocular filters have a denser coating since high magnifications are not used.

Mounting: The inside of the cell will be lined with felt or unlined depending on the telescope brand and aperture. If your filter is too loose, it can be custom fitted using felt or tape on inside of cell. The filter should not fit too tightly or the optical surface may be distorted due to stress on the cell. If you have purchased an unmounted filter and will be mounting it in your own cell, be sure to mount it in such a way as to allow for thermal expansion and contraction. The glass should not be firmly cemented or clamped within the cell or holder.

CAUTION: If you do not have a solar filter for your finder-scope, keep it covered. Looking through the finder-scope at the sun without a proper filter can damage your eye in a fraction of a second. With a little practice you can obtain a close alignment by moving your tube assembly until the smallest shadow of the tube assembly is cast behind you.

Solar Photography: All of our standard glass and Polymer solar filters are coated to a neutral density of 5, which reduces the light about 100,000 times. Depending on the aperture and focal length of your telescope and "seeing" conditions, you will need to experiment to find the best exposure time for your equipment. We recommend starting with a 100 to 200 ISO film such as Kodak Ektachrome color slide film.

At prime focus, start with an exposure of about 1/250 second using the above or similar film. Experiment with different shutter speeds as well. When using higher magnifications, longer exposures will generally be necessary. Be sure to keep notes on how each frame was exposed so you can compare after the film is processed. Try experimenting with other films as well. If you are a beginner in astrophotography and need further information, there are books available that cover this subject completely. These books can be found at your local bookstore or library and from suppliers listed in the popular astronomical publications.

Type 3+ - These filters are designed for "seasoned" astrophotographers for use with very fine grain films without the necessity of increased exposure times. The transmission is about 1/100th of 1% and should not be used visually, except when focusing through the camera.

Do not be discouraged if your first attempts at solar photography are less than desired. The sun is very difficult to photograph because of poorer "seeing" conditions caused by unavoidable heat currents inherent with daytime viewing. The highest possible resolution for any land based telescope, regardless of location, is about 1 arc second. Ideal seeing for any location will be available less than 5% of the time. During bad seeing conditions, it may help to "stop down" full aperture filters over 5".


  • Check filter for any possible damage before each use.
  • Keep the finder-scope covered if not equipped with a solar filter.
  • Allow telescope and filter to equalize to outside temperature (at least 15 minutes).
  • Direct sunlight may warm the tube assembly enough to cause internal heat currents that can degrade image quality. Cover the tube assembly with a light colored cloth.
  • If possible, do not view over pavement or buildings. Viewing over grass will help avoid surface heat currents.
  • Point telescope away from sun before removing solar filter.
  • Do not leave telescope unattended where children or inexperienced adults could point it at the sun without the filter properly attached.
  • As with any optic, clean coated surface only if absolutely necessary.
  • "Ghosting" can occur due to internal reflections. If this is a problem, simply tilt the filter slightly. (Glass only)
  • Do not place your filter up against a smaller telescope. The end of the tube will damage the coating or substrate.
  • When looking through the focusing tube without an eyepiece, there may appear to be small defects in the coating which are not seen when observing through the eyepiece. This is normal and is not a coating defect or safety concern.

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